Evidence of Spin-Forbidden Excitation of [Ru(bpy)3]2+ and Application in Red-Light-Driven Photocatalysis

Red-light-driven catalysis presents a promising alternative to conventional blue light photocatalysis, offering enhanced light penetration, functional group tolerance, and energy efficiency. However, its widespread application remains underdeveloped, partly due to the lack of readily accessible photocatalysts capable of efficiently absorbing low-energy red photons. A promising, yet underexplored, strategy involves direct spin-forbidden singlet-to-triplet excitation. In this study, we demonstrate the experimental evidence that [Ru(bpy)₃]²⁺ can engage in photocatalysis through direct singlet-to-triplet excitation under red light irradiation. This finding, supported by optical and spectroscopic investigations, broadens the reactivity of [Ru(bpy)₃]²⁺ and offers broadly applicable design principles for robust Ru(II) photocatalysts suited for red-light-driven reactions.